A quick google search shows that you have to set the IP of the Nagios server connecting to nrpe by modifying the "allowed_hosts" section of nrpe.cfg. Have you done that? If so, what does dmesg say? Have you tried running the nrpe check command from the terminal directly?
/usr/local/nagios/libexec/check_nrpe -H remotehostIP
There's a sample for how you could do it.